You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Ankle, Flexor Hallucis Longus Tendon InjuriesArticle Last Updated: Jul 31, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Stacy E Smith, MD, Associate Professor of Radiology, Division of Musculoskeletal Imaging, University of Maryland School of Medicine Stacy E Smith is a member of the following medical societies: American Association for Women Radiologists, American College of Radiology, American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America, and Society of Skeletal Radiology Coauthor(s): Christopher W Flye, MD, Consulting Staff, Coastal Radiology Associates PLLC Editors: Amilcare Gentili, MD, Clinical Professor of Radiology, University of California at San Diego; Consulting Staff, Department of Radiology, Thornton Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Thomas Lee Pope Jr, MD, FACR, Professor of Radiology and Orthopedics, Department of Radiology, Medical University of South Carolina; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related keywords: FHL, dancer's tendinitis, posterior impingement syndrome, checkrein deformity INTRODUCTIONSection 2 of 12
  BackgroundInjuries to the flexor hallucis longus (FHL) tendon have classically been described in ballet dancers secondary to their constant repetitive plantar flexion. Hence, the injury is often called dancer's tendinitis. Such injuries have also been described in association with climbing, soccer, and running in relation to frequent push-off maneuvers of the forefoot in these activities. FHL tenosynovitis is infrequently seen in association with other conditions, such as diabetes, rheumatoid arthritis, lupus, and seronegative spondyloarthropathies. PathophysiologyPathology of the FHL tendon is commonly related to overuse. Direct trauma and, less commonly, inflammatory disease are other causes. Types of injuries with associated definitions include the following:
Particularly in ballet dancers, repetitive and prolonged plantar flexion leads to tenosynovitis or tendinopathy. With further overuse, progression to frank longitudinal tears can occur. Inflammation of the FHL tendon generally occurs in 1 of 3 areas: (1) at the fibro-osseous tunnel along the posteromedial ankle, (2) under the base of the first metatarsal where the flexor digitorum longus (FDL) tendon crosses the FHL tendon (known as the knot of Henry), or (3) where the FHL tendon passes between the great toe sesamoids beneath the metatarsal head. When the tendon becomes nodular, triggering of the great toe (hallux saltans) may develop, and progression to hallux rigidus may occur. Complete tears of the FHL tendon are rare, with fewer than 4 cases of acute rupture reported in the literature. Two were reported in athletes with acute trauma within 1 cm of the tendon insertion: 1 at the distal border of the tarsal tunnel in a high-level athlete with continued overuse and 1 in a patient with history of rheumatoid arthritis with spontaneous atraumatic rupture under the sustentaculum tali. Entrapment of the flexor hallucis tendon may be due to an enlarged os trigonum, an associated calcaneal fracture or fracture dislocation (first reported in 1960 in Barcelona by Jimeno-Vidal), or soft-tissue scar after injury or surgery. Entrapment of the musculotendinous junction secondary to callus has also been reported after fibular fracture fixation. One case report of intermittent dislocation is noted in the literature. The 2 hypotheses provided for such an event include hypoplasia of the posteromedial process of the talus and weakness of the fibrous retinaculum. FrequencyUnited StatesUnlike the posterior tibialis and Achilles tendons, the FHL tendon is among the tendons least commonly injured. Numeric details in the United States are not available, though these injuries are most frequently seen in ballet dancers and athletes (eg, downhill runners) who require repetitive push-off of the forefoot. Mortality/MorbidityUnrecognized injuries to the FHL tendon can lead to chronic pain, early arthritis, and fibrosis with resultant decreased range of motion over time. In elite athletes, particularly in athletes who repeatedly used plantar flexion maneuvers, determination of the degree of injury to the FHL or its surrounding structures is paramount because loss of their livelihood is at stake. RaceNo particular race predilection has been noted. SexNo particular sex delineation is noted. AgeInjuries to the FHL tendon and its surrounding structures tend to most commonly occur in young athletes. However, recreational athletes ("weekend warriors") may have chronic tendinopathy and, in rare cases, acute tears. Abnormalities of and injuries to the FHL tendon without seemingly extreme exertion may occur over a larger age range in predisposed individuals, such as those with diabetes, rheumatoid arthritis, seronegative arthropathies, or lupus. AnatomyThe FHL muscle is the most lateral muscle of the deep compartment of the calf originating from the lower two thirds of the posterior surface of the shaft of the fibula, with its distal tendinous insertion on the distal phalanx of the great toe. The FHL tendon itself begins just above the level of the medial malleolus and lies posterolateral to the posterior tibialis and FDL tendons in the posterior medial aspect of the ankle. All 3 tendons course in the fibro-osseous tunnel behind the medial malleolus and beneath the flexor retinaculum; they then pass through the tunnel between the medial and lateral talar tubercles of the posterior talus, which is lined by a synovial sheath. The FHL then enters the foot by crossing the posterior subtalar joint and passing under the inferior aspect of the sustentaculum tali, analogous to a rope through a pulley. The tendon then converges medially, crossing the FDL tendon in the middle plantar compartment with the FDL tendon positioned plantarly. This area where the FHL and the FDL tendon cross over in the foot is called the knot of Henry; this is located approximately 1 thumb breadth lateral to the tuberosity of the navicular. A tendinous slip of the lateral portion of the FHL tendon joins with the FDL tendon in the sole of the foot, providing a tethering mechanism. This prevents excessive retraction of a proximal FHL tendon fragment after rupture. In its distal aspect, the FHL tendon crosses the lateral belly of the flexor hallucis brevis muscle and lies superficial to and between the 2 heads of the flexor hallucis brevis muscle at the intersesamoid interval of the great toe, inserting into the base of the distal phalanx. The tibial nerve innervates the FHL muscle and tendon. Clinical DetailsDancers usually present with an insidious onset of posteromedial ankle pain, which is occasionally associated with localized swelling. Initial treatment is conservative with physical therapy, use of nonsteroidal anti-inflammatory drugs (NSAIDs), and alteration of exercise and activity. When medical therapy fails and symptoms persist unimproved after 3-6 months, surgical exploration and treatment may be required to repair any tears, excise nodules, and perform fibroosseous tunnel release, among other indications. Preferred ExaminationPhysical examination is the initial evaluation for the patient with posteromedial ankle pain. To allow complete dorsiflexion at the ankle, the knee is flexed 90° to relax the gastrocnemius. The knee is then extended with plantar flexion of the ankle and great toe, with the clinician palpating behind the medial malleolus. These maneuvers can allow differentiation of tendinitis (diffuse tenderness or crepitation) from causes of trigger toe and hallux rigidus. Triggering occurs when a nodular thickening of the tendon snaps through the fibro-osseous tunnel. This is generally palpable. Hypertrophy of the FHL at the musculotendinous junction may produce hallux rigidus, with restriction of dorsiflexion of the hallux. Computed tomography (CT) is best for precisely depicting the ossific anatomy and the gross size and location of the tendon. However, because of its multiplanar and multisequence capabilities, MRI helps in clarifying tendinous findings, such as coexistent tenosynovitis, tendinopathy, partial or complete tears, and associated fluid. In addition, magnetic resonance imaging (MRI) permits characterization of the anatomy of the fibrous retinaculum. Bone marrow edema is best evaluated with MRI and may help in identifying an os trigonum syndrome or contusions of adjacent bones. DIFFERENTIALSSection 3 of 12
Ankle, Tibialis Posterior Tendon Injuries Other Problems to Be ConsideredPosterior impingement syndrome
RADIOGRAPHSection 4 of 12
FindingsRadiographic findings include soft-tissue swelling at the posteromedial aspect of the ankle. This finding is usually nonspecific, and an associated joint effusion may be present. Fractures of the calcaneus, distal medial malleolus, or os trigonum may suggest an abnormality of the FHL tendon, as all 3 have been reported in association with FHL tendinopathy, partial and complete tears, entrapment, and dislocation. Degree of ConfidenceRadiography provides a low degree of confidence for definitive diagnosis because the tendon itself is not visualized. However, radiography offers a moderate degree of confidence in identifying the ancillary findings described above that may raise the suspicion for FHL injury and can identify the presence of an os trigonum. False Positives/NegativesFalse-positive results may involve a focal area of soft-tissue swelling secondary to hematoma rather than tendon injury because soft tissues are not well delineated with this modality. Lack of findings on the radiograph do not preclude further advanced imaging, such as CT or MRI, as these are best suited for fine analysis of the soft tissues. CT SCANSection 5 of 12
FindingsCT can be useful in evaluating the presence, location, size, and anatomy of the FHL tendon, as well as in eliciting any fluid in the synovial sheath. The normal tendon is round or slightly oval, with intermediate homogeneous density. About 20% of healthy patients may have fluid in the tendon sheath, because the FHL tendon sheath communicates with the ankle joint. Absence of the tendon or complete discontinuity of the tendon suggests tear with retraction. Thickening or heterogeneous attenuation suggests either tendinopathy or partial tear or healing remote injury. Increased abnormal fluid in the tendon sheath is highly suggestive of FHL entrapment. Ossific anatomy, such as associated fractures (particularly calcaneal or posterior talar or tibial), an os trigonum, and foreign bodies, are best evaluated with this modality. Degree of ConfidenceCT offers a moderate degree of confidence because an abnormal size and attenuation in the tendon with associated fluid are seen in injuries of the FHL. However, the fine detail, such as delineation of tendinopathy versus partial tendon tear, is best assessed with MRI. Complete tears can be detected on CT if the torn ends of the tendon are retracted. False Positives/NegativesFocal thickening of tendons such as xanthomas or fibrous nodules can mimic focal areas of tear or tendinopathy. MRISection 6 of 12
FindingsIn conjunction with physical examination and clinical history taking, MRI can be helpful in evaluating FHL tendon injuries. MRI may easily show abnormal signal intensity in tendons, the intactness of fibers, and the size of the tendon, as well as any surrounding fluid. Adjacent bone marrow edema, contusion, inflammation, or nondisplaced fractures are also best visualized with this modality. Axial proton density (PD)– and T2-weighted fat-saturated fast spin-echo (FSE) sequences, as well as sagittal inversion-recovery (IR) or T2-weighted fat-saturated FSE and T1-weighted sequences of the ankle (which includes the foot to the base of the distal phalanx of the great toe), are best for evaluating the FHL tendon. The FHL is best seen just lateral to the posterior tibialis tendon as it curves around the sustentaculum. Coronal images can help evaluate adjacent bone, soft tissue, or tendons. After clinical examination, an MRI can be performed to confirm or further delineate the exact location and extent of the abnormalities. Three areas of tendinopathy are (1) posterior to the talus in the region of the fibroosseous tunnel (classic type), (2) the knot of Henry under the base of the first metatarsal, and (3) the head of the first metatarsal where the tendon passes between the sesamoids. MRI can help identify tendinopathy in the classic location due to an anatomic variant (short tendinous region of FHL with long distal muscle belly) or due to direct irritation. Direct irritation is seen on MRI as irregular fraying, fusiform enlargement, cystic changes, and/or nodule formation in the tendon. Tenosynovitis may be present either alone or in combination with FHL tendinopathy. Isolated fluid in the synovial sheath may indicate tenosynovitis. However, as noted, this finding can be a normal variant in up to 20% of patients, but increased fluid is suggestive of tenosynovitis. Partial tendon tears show intrinsic longitudinal marked hyperintensity and fusiform tendon thickening on T2-weighted fat-saturated or IR MRI. The MRI findings of complete tendon tear include fluid signal intensity between the torn ends of the tendon or between the musculotendinous junction and the tendon, with minimal or marked retraction and or undulation of the tendon ends. Soft-tissue edema and swelling may also be seen. If the tear is due to inflammatory changes, other associated findings (eg, synovial thickening due to rheumatoid arthritis) may be seen. Complete entrapment with acute tears may show associated bone marrow edema. MRI signs of entrapment include the following: tendon entrapment or tethering by bone or soft tissue, abrupt cutoff of the synovial fluid of the FHL tendon sheath with differential volumes of fluid (hyperintensity on T2-weighted or IR MRIs) above and below the site of entrapment, and alteration of the size or signal intensity of the tendon morphology. Prominent areas of persistent hypointense callus around a fracture or fractures that have been treated with surgery can be noted as the cause of entrapment; these are most often complete (checkrein deformity). Os trigonum syndrome is one cause of partial entrapment or tethering of the FHL tendon (see below). An unfused lateral tubercle of the posterior talus found just lateral to the fibro-osseous tunnel may be seen in 14-25% of the population. The size of the tubercle is not usually a predictor of clinical symptoms. However, increased bone marrow edema or fluid around the posterior talus, an os trigonum, adjacent calcaneal and synovial sheath fluid, or tendon signal change suggests os trigonum syndrome as the cause of posteromedial ankle pain, especially when heterogeneous signal changes are noted in the FHL tendon. Correlative clinical reproduction of pain in extreme plantar flexion or maximum dorsiflexion of the great toe with resistance is usually present and helps support this diagnosis. Tendon dislocation is a straightforward diagnosis on MRI, as the tendon lies outside the posterior intertubercular groove. However, if the patient has a voluntary snap of the posterior medial ankle triggered by maximal ankle dorsiflexion and interphalangeal plantar flexion of the toes, axial PD-weighted and T2-weighted fat-saturated FSE MRI in static and dynamic positions can help make the diagnosis of the rare intermittent dislocation of the FHL tendon. Degree of ConfidenceMRI offers a high degree of confidence with respect to FHL tendon injuries. The multiplanar and multisequence capabilities of MRI allow the distinction to be made between tendinopathy partial tear and complete tear and can demonstrate abnormal intrinsic signal intensity versus fluid in the tendon sheath (tenosynovitis). This modality also allows visualization of possible alternative anatomic causes of the clinical symptoms that may mimic injuries of the FHL tendon. False Positives/NegativesIn rare cases, abscesses or masses of the tendon or tendon sheath may mimic injuries to the FHL tendon. However, the degree of signal intensity usually helps in differentiating a true abscess around a tendon from true tendinopathy or partial tear (acute or chronic). ULTRASOUNDSection 7 of 12
FindingsAlthough ultrasonography is commonly used to evaluate injuries of the Achilles tendon, the posterior medial location of the FHL tendon makes evaluation with sonography more problematic. However, the utility of sonography is in the ability to examine the patient at rest and in dynamic flexion and extension. Transverse and longitudinal scans at the level of the medial malleolus posteriorly allow visualization of the size, echogenicity, and location of the tendons with relation to one another. Associated fluid collections can also be seen as lobular areas of lower echogenicity surrounding the tendon or in the ankle joint. A thickened, heterogeneous tendon suggests tendinopathy. Complete absence of the tendon, disappearance of the tendon or retraction of the ends of the FHL tendon between rest and dynamic flexion studies of the tendon in the prone position, and a fluid-filled gap between the ends of the tendon are consistent with a tendinous tear. The medial flexor group lies adjacent to the hyperechogenic cortical rim of the medial malleolus. The FHL tendon is normally slightly smaller and located medial to the FDL tendon just posterior to the malleolus. The FHL tendon and muscle are posterior to the posterior tibial border and are separated from the Achilles tendon by the Kager triangle. Degree of ConfidenceWith skilled and trained operators, sonography offers a moderate-to-high degree of confidence in diagnosing abnormalities of the FHL tendon, providing detailed images of the tendon and surrounding soft-tissue structures throughout most of the course of the tendon itself. Adjacent ossific structures are noted but are better depicted on radiographs, CT scans, and MR studies. Subtle changes in the position of the transducer during the examination may cause artifacts. Subtle anatomic abnormalities previously unknown to the examiner may also obscure or preclude complete imaging of the area. The normal anatomy and course of the tendon are fairly straightforward. However, the distal pathway between the sesamoid bones may be difficult to image if the appropriate high-resolution transducer is not available. False Positives/NegativesSee Degree of Confidence, above. NUCLEAR MEDICINESection 8 of 12
FindingsAt present, nuclear medicine has a limited role in the evaluation of tendon injuries other than showing areas of increased tracer uptake in the area of soft-tissue injury. It may be of benefit in depicting other abnormalities of bone (infection or fracture). However, MRI is more sensitive and specific than nuclear medicine studies for this purpose. WBC nuclear scans may be sensitive to infection of the tendon or adjacent bone and direct treatment with regard to antibiotics, rather than just physical therapy for traumatic injury. ANGIOGRAPHYSection 9 of 12
FindingsAngiography is not needed to assess or diagnose FHL tendon injuries. INTERVENTIONSection 10 of 12
Although no radiologic intervention is generally required, steroid injection under ultrasonographic guidance may alleviate pain and discomfort in some cases for short-term management of chronic tendinopathy or tenosynovitis. Most commonly, conservative management (immobilization, activity restrictions, and use of NSAIDs) is the treatment of injuries to the FHL tendon (tendinopathy, tenosynovitis, and partial tear); an exception is a complete tear with marked retraction. In cases of complete tears, some surgeons administer a trial of conservative treatment. However, surgical repair with reapposition of the torn ends of the tendon is eventually performed. In patients with chronic dislocation or subluxation, surgery is reserved for those in whom conservative therapy fails or for high-level athletes. If an anatomic abnormality led to the FHL injury, resection of abnormal ossific structures, repositioning of hardware, or fixation of fractures in patients with previous ankle and foot fracture may be required. Medical/Legal Pitfalls
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Ankle, Flexor Hallucis Longus Tendon Injuries excerpt Article Last Updated: Jul 31, 2007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
